Cold wire thermometry for turbine measurements

The aim of this work is the characterization of the dynamic behaviour of a cold wire. The probe has been first calibrated in static conditions in two different ways (oven and heated jet); the dynamic calibration has been realized with temperature step tests. In these tests a shield has been used to isolate the cold wire from an air-heated jet of a certain temperature and Mach number: the shield has been removed abruptly with a finite velocity thus exposing the transducer to the jet. In this way it has been realized a ‘step’ of temperature. This experimental test has been compared to the theoretical step and it was possible to get the transfer function describing the dynamic behaviour of the cold wire at low frequencies. The obtained transfer function has been modified adding the contribution of the tungsten wire in order to take into account the high frequencies: the wire behaves like a first order system whose transfer function can be obtained analytically. The compensation has been obtained using the inverse of the transfer function. Finally the cold wire has been tested in a turbine running at 2200 rpm in vacuum-ambient pressure transient conditions in order to see the effects of compensation.